Method for decomposing sulfuric acid sludge



Aug. 25,v 1964 w. H. LITCHFIELD 3,146,067

METHOD FOR DECOMOSING SULFURIC ACID SLUDGE Original Filed June 18, 1958"c 1 40 [25 /6/ o /a I if 42 I .52 a (LP .ae I 1 @[5 ,/1 sa) 2z 30 L 50j N -L L d E E 46 .g 33 t 2226i. 1 2044 "'&- l d 48 a4 a ffzffag UnitedStatesv Patent O "ice 3,146,067 METHOD FOR DECUMPOSING SULFURIC AClDSLUDGE William H. Litchfield, Port Arthur, Tex., assignor to Gulf OilCorporation, Pittsburgh, Pa., a corporation of Pennsylvania Originalapplication June 18, 1958, Ser. No. 742,946, now Patent No. 3,060,005,dated Oct. 23, 1962. Divided and this application Feb. 15, 1962, Ser.No. 173,547

3 Claims. (Cl. 23-177) This invention relates to an improved method forrecovering valuable products for sulfuric acid sludges, moreparticularly a method of recovering valuable products such as sulfurdioxide and a carbonaceous material commonly referred to as coke fromsulfuric acid sludges resulting from the reiining of petroleum products.

Sulfuric acid is employed widely and in large amounts in theconventional refining of petroleum hydrocarbons. As a result of suchtreatment acid sludges consisting essentially of sulfuric acid,sulfonates and hydrocarbon material are formed. Examples of sulfuricacid sludges produced in the petroleum industry as a result of retiningpetroleum are spent alkylation acids, sludge from pressure stilldistillate treatment, sludge from lube oil treatment, sludge from waxtreatment, sludge from treatment of kerosene, etc. Since the amount ofsulfuric acid sludge produced in the petroleum industry is large, and amajor portion thereof consists of sulfuric acid, it is apparent that therecovery of sulfuric acid values therefrom is a great importance.

In the past, sulfuric acid values from sulfuric acid sludge have beenrecovered by heating the sludge to a temperature in excess of about 500F. for a time sufcient to decompose the same into gaseous productscomprising sulfur dioxide, water and hydrocarbon vapors and acarbonaceous material commonly known as cokef The heat required tomaintain decomposition temperatures has been obtained in many ways. Inthe present case, for example, heat is obtained in two ways. First, heatis supplied for decomposition of the sulfuric acid sludge by burnersmaintained in indirect heat exchange relationship with the sludge withinthe decomposition zone.

Second, a large amount of the coke which is formed in the decompositionzone is withdrawn therefrom at an elevated temperature, which can beabout 400 to about 500 F., and recycled to the decomposition zone tosupply additional heat.

The hot coke which is recycled is not reintroduced into thedecomposition zone as such, but was previously passed therein along withthe sulfuric acid sludge to be decomposed. The sulfuric acid sludge isgenerally in the form of a liquid, While the coke is a particulatecarbonaceous material. Unfortunately when the hot coke and sludge arethoroughly mixed before entering the decomposition zone, for example, ina conveyor with forward and reversing paddles (but in some cases a screwconveyor) large balls of gummy material are formed and/or a heavydeposit is built up on the paddles or screw, plugging the conveyor.Other methods of combining the sludge and coke result in formation oflumps in the decomposition zone or kiln, where they must be broken up tokeep the decomposition zone from being clogged. This requires the use ofadditional equipment in the decomposition zone and further complicatesthe decomposition process. In addition, since the recycled coke is hot,a small amount of decomposition of the for example, heat is obtained intwo ways. First, heat sludge occurs in the feed screw conveyor whencontact is made between the coke and sludge. The gas resulting from thedecomposition, comprising sulfur dioxide, hydrocarbon vapors, watervapor, etc., is wet and wets 3,146,067 Patented Aug. 25,` 1964 thesurfaces of the screw conveyor as well as the walls of the chamber inwhich it is located. Further wetting of the surface of the conveyor andthe walls of the chamber can occur from splashing of the sludge whenintroduced into the chamber. The recycled coke is in particulate formand will deposit on the wet surfaces and walls. In a short time thesedeposits will build up and clog the screw conveyor.

While some advantage has been obtained in this respect by following theprocedure set forth in Application Serial No. 581,623 of Arthur H.Catanach, now US. Patent No. 2,894,819, periodic formation of gummyballs and/ or heavy deposits are still built up after a time on thepaddles or screw of the feed conveyor. Although such procedure involvesfar less shut-down than formerly, any shut-down is costly and can bedestructive to machinery.

I have found that the above-noted difficulties in the conveyor can beeliminated and the formation of gummy balls in the decomposition zone orkiln can be substantially avoided, while recovering acid values fromsulfuric acid sludge, by a process which involves introducing hot cokedmaterial into said decomposition zone, separately introduced sulfuricacid sludge into said decomposition zone and spraying the same on thehot coked material to form a coating on said hot coked material,maintaining the temperature in said decomposition zone suiciently highto substantially coke the major portion of the hydrocarbon material insaid sludge and obtain gaseous decomposition products, removing saidgaseous decomposition products from said decomposition zone, removingcoked material from said decomposition zone, and recycling a portion ofsaid latter coked material to constitute the hot coked material coatedwith the sulfuric acid sludge.

Any sulfuric acid sludge can be subjected to the method of the presentinvention with good results providing the carbon content of the sludgeis high enough to maintain sufficient coke for recycle. Spent alkylationacid of about five per cent total carbon content cannot be charged byitself for this reason but must be mixed with a higher carbon contentacid sludge. As examples of sulfuric acid sludges which can be employedcan be mentioned spent alkylation acids, sludge from pressure stilldistillate treatment, sludge from lube oil treatment, sludge from waxtreatment, sludge from treatment of kerosene, etc., or mixtures thereof.The temperature of the sulfuric acid sludge is not critical, though itshould be high enough to permit it to be pumped but not so high as toobtain any appreciable decomposition thereof. In general, the sludge tobe treated should be at a temperature of about 60 to about F. While, asnoted, any conventional sulfuric acid sludge can be treated in theprocess of this invention, best results are obtained when the sludgecomprises about 35 to about 85 percent by weight of sulfuric acid, acarbon content of about 10 to about 50 percent by weight, and about 0 toabout 15 percent by weight of water.

The average particle size of the recycled coke is generally below about1% inch in diameter, preferably between about 1/16 and 1/4 inch indiameter. The temperature of the coke leaving the decomposition zone canbe about 400 to about 500 F., but is preferably about 420 to about 460F. If the temperature of the recycled coke were permitted to drop belowabout 400 F., the coke would contain some free acid and someundecomposed sludge. The amount of coke which must be recycled to obtaingood results is about 15 to about 30, preferably about 20 to about 25,parts by weight of coke per part by Weight of sludge. Within theseranges, the amount of sludge is sufficient to coat or substantially coata large proportion of the coke particles.

The temperature in the decomposition zone can be as low as about 500 F.or as high as about l200 F., but preferably is about 700 to about 800 F.The pressure is not critical and can vary from about atmospheric toabout four inches water vacuum, a pressure of about onehalf inch ofwater vacuum having found very satisfactory. Residence time of thesludge in the decomposition zone will depend upon many variables, ofcourse, such as the quality of the sludge being treated, the temperaturein the decomposition zone, etc., but in general a period of about two toabout minutes has been found to be suicient.

In order to obtain the beneiicial results of the present invention, themanner in which the hot coked material which is introduced into thedecomposition zone is coated with the sulfuric acid sludge is extremelycritical. In order to effect the desired coating of the hot cokedmaterial with the sulfuric acid sludge, the two are introducedseparately into the decomposition zone. The hot coked material after itsintroduction into the decomposition zone is spread onto the floor of thehearth to form a thin layer of the same. To facilitate the coatingoperation, the layer of hot coked material must possess an averagethickness of about one to about nine inches, preferably about two toabout six inches. The sulfuric acid sludge is introduced into thedecomposition zone in the form of a finely-divided spray, such as can beobtained by use of a spray nozzle. The nozzle employed should beselected, preferably, to give maximum atomization of the sulfuric acidcharged. Most important, in order to obtain maximum coverage of the cokesurface and not impinge upon the walls of the decomposer or the rabblearms of the spreader therein and form gummy balls of coked material, itis critical in the practice of this invention to introduce the sulfuricacid sludge in the decomposition zone in a spray pattern having about an88 to about 92, preferably about a 90 cone. One edge of said cone issubstantially perpendicular to the layer of coke. By operating inaccordance with the above no appreciable deposits of sulfuric acidsludge will form in the decomposition zone, which would be likely toform gummy material, and about 70 to about 100 percent by weight of thehot coked material will be substantially completely coated with thesulfuric acid sludge.

The process of this invention can be illustrated by reference to theaccompanying drawing which is hereby incorporated in and made part ofthe present specification. In FIGURE 1, there is illustrated a somewhatdiagrammatic view in elevation of a decomposer, partially in section,which can be employed in the process of this invention. FIGURE 2 is alsoa somewhat diagrammatic view taken along the line II-II in FIGURE l.

Finished coke 2 leaves decomposer 4, substantially circular incross-section, by way of conduit 6 and is moved in any convenientmanner, as by screw conveyors 8 and 10, into a hopper 12 having twosections 14 and 16. That portion falling into section 14 constitutes thenet make of coke and is withdrawn from the system through outlet 18,while that portion falling into section 16 is picked up by screwconveyor, or other similar conveying means, 20 and returned todecomposer 4.

The coke particles which are recycled to the decomposer 4 fall onto theupper floor 22 thereof. Rabble arms 24, preferably provided with teeth26, which are xedly mounted on rotating shaft 28 rotating in thedirection of the arrow encircling it, spread the coke particles acrossthe upper floor 22 of the hearth to form a thin layer thereof whilesimultaneously moving the coke particles toward the center of the upperoor. As stated, in order to facilitate the coating of the individualcoke particles with sulfuric acid sludge, the layer of the coke ismaintained at an average thickness of about one to about nine inches,preferably about two to about six inches.

While it is critical in the practice of my invention to spread the cokeon upper oor 22 in the manner set forth above, it is equally criticalthat the sulfuric acid sludge be introduced onto the layer of coke inthe form of a finely-divided spray. This can be effected by using aspray nozzle 30. The spray pattern employed is equally critical, becauseit is absolutely necessary that there be little or no sulfuric acidsludge collecting on rabble arms 24 or the walls of the decomposer 4 ifthe formation of gummy and carbonaceous balls is to be avoided. To thisend the spray pattern of sulfuric acid sludge entering the decomposer 4is preferably one having about a 90 cone, although in some cases thecone can be as low as about 88 or as high as 92.

As the coke is coated with sulfuric acid sludge and moves toward shaft28, it drops on the lower floor 32 wherein rabble arms 34, preferablyprovided with teeth 36, also fixedly attached to shaft 28, move thecoated particles outwardly toward conduit 6 for removal from thedecomposer. While the thickness of the layer of coke on lower oor 32 isnot as critical as the thickness of the layer on the upper floor, it isgenerally maintained at about the same thickness, preferably tofacilitate heat transfer to each of the particles forming the layer. Bythe time the coated particles have moved toward the perimeter of loweroor 32 and are ready to drop into conduit 6, the sludge introduced intothe decomposer has decomposed to form additional carbonaceous materialand gaseous products such as sulfur dioxide, hydrocarbon vapors, carbondioxide and nitrogen. Heat for the decomposition is supplied to thedecomposer 4 by the hot recycled coke and by burners 38, employingnatural gas or the like, mounted in indirect heat exchange relationshipwith respect to the sludge within the decomposition zone itself. Exhaustgases from the burners are removed by line 40, while the decompositiongases are removed by line 42 for further processing.

The amount of sludge that can be charged to the decomposer is limited bythe amount of heat that can be transferred into the decomposition zone.In order to get more heat into :the decomposition zone, I can add heatto the recycle coke prior to its entry into the decomposition zone inany convenient manner. Thus a jacket 44 can be provided around screwconveyor 1t) with hot gases entering line 46 from line 40 and leaving byline 48. In addition or in place of jacket 44, a similar means 50 can beprovided in the line below hopper 12, with hot gases entering line 52from line 40 and leaving by line 54.

The process of this invention can further be illustrated by -thefollowing example. Over a twenty-four hour period, 18,000 pounds of coke(net make) having an average diameter of about Mt inch to 1/0 inch and atemperature of 490 F. were removed from the decomposition zone. rfhecoke was recycled at the rate of 23 cubic feet per minute (about 911tons per day) and introduced into the decomposition zone wherein rabblearms spread the coke on the upper iioor of the hearth to form a layerthereof having an average thickness of 2 inches. The sulfuric acidsludge, at a rate of 55 pounds per minute, was introduced into thedecomposition zone inthe manner illustrated in FIGURE l in the form of afinely-divided spray with a spray pattern having a Cone. The sulfuricacid sludge analyzed as follows: 45.2 percent by weight of sulfuricacid, 6.5 percent by weight of water and 38.2 percent by weight ofcarbon. The temperature in the decomposition Zone was maintained at 750F., the pressure 0 inch of water and the residence time 8 minutes. Thedecomposition gases analyzed as follows: 76.3 percent by volume sulfurdioxide, 12.4 percent by volume hydrocarbons, 4.1 percent by volumecarbon monoxide, 6.6 percent by volume carbon dioxide and 0.6 percent byvolume nitrogen. The process described was in operation 238 days withoutshutdown for removal of balls of gummy material or other heavy deposits.

, on. "If

The application is a divisional application of my application Serial No.742,946, filed June 18, 1958, now U.S. Patent No. 3,060,005.

Obviously, many modifications and variations of the invention, ashereinabove set forth, can be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

I claim:

l. Method for recovering acid values from sulfuric acid sludge whichcomprises introducing hot coked material into a decomposition zone,immediately spreading said hot coked material to form a layer having anaverage thickness of about one to about nine inches, spraying atomizedsulfuric acid sludge onto said layer at the point of entry of said hotcoked material into said decomposition zone to coat said hot cokedmaterial while maintaining a spray cone pattern of about 88 to about 92,one edge of said cone being substantially perpendicular to said layer,maintaining the temperature in said decomposition zone suiiciently highto substantially coke the major portion of the hydrocarbon material insaid sludge and obtain gaseous decomposition products, removing saidgaseous decomposition products from said gaseous decomposition z-one,removing coked material from said decomposition zone and recycling aportion of said latter coked material to constitute the hot cokedmaterial coated with the sulfuric acid sludge.

2. Method for recovering acid values from sulfuric acid sludge whichcomprises introducing hot coked material into a decomposition zone,immediately spreading said hot coked material to form a layer having anaverage thickness of about one to about nine inches, spraying atomizedsulfuric acid sludge onto said layer at the point of entry of said hotcoked material into said decomposition zone to coat said hot cokedmaterial While maintaining a spray cone pattern of about 88 to about 90,one edge of -said cone being substantially perpendicular to said layer,maintaining the temperature in said decomposition zone sufficiently highto substantially coke the major portion of the hydrocarbon material insaid sludge and obtain gaseous decomposition products, removing saidgaseous decomposition products from said gaseous decomposition zone,removing coked material from said decomposition zone and recycling aportion of said latter coked material to constitute the hot cokedmaterial coated with the sulfuric acid sludge.

3. Method for recovering acid values from sulfuric acid sludge whichcomprises introducing hot coked material into a decomposition zone,immediately spreading said hot coked material to form a layer having anaverage thickness `of about one to about nine inches, spraying atomizedsulfuric acid sludge onto said layer at the point of entry of said hotcoked material into said decomposition zone to coat said hot cokedmaterial While maintaining a spray cone pattern of about one edge ofsaid cone being substantially perpendicular -to said layer, maintainingthe temperature in said decomposition zone at about 500 to about 1200 F.to substantially coke the major portion of the hydrocarbon material insaid sludge and :obtain gaseous decomposition products, removing saidgaseous decomposition products `from said gaseous decomposition zone,removing coked material from said decomposition z-one at a temperatureof about 400 to about 500 F. having :an average particle size less thanabout 3/ inch in diameter, land recycling a portion of said latter cokedmaterial to constitute the hot coked material coated with the sulfuricacid sludge, the amount of recycled coked material being about 15 toabout 30 parts by Weight per part of sulfuric acid sludge.

References Cited in the file of this patent UNITED STATES PATENTS1,976,528 Vandeveer Oct. 9, 1934 2,086,733` Mullen July 13, 19372,223,934 Barnes et al. Dec. 3, 1940 2,894,819 Catanach July 14, 1959FOREIGN PATENTS 669,209 Great Britain Mar. 26, 1952 UNITED STATES PATENTFFICE CERTIFICATE 0E CORRECT IN Patent No, 3,146,067 August 25, 1964william H, Litchfield It is hereby certifiedl that' error appears in theabove numbered patentv requiring correction and that the said LettersPatent should read as corrected below.

Column l, line l2, for "for" read from line 13, for "of" read for line30, for "a" read of line 67, strike out "for example, heat is obtainedin two ways,I First, heat"; column 2, line l5, for "shut-down" readshutdowns line 24, forfintroduced" read introducing column 3, line 8,after "having" insert been Signed and sealed this 29th day of December1964.,

(SEAL) Attest:

ERNEST w. swIDER EDWARD J. BRENNER Alu-,sting Officer Commissioner ofPatents

1. METHOD FOR RECOVERING ACID VALUES FROM SULFURIC ACID SLUDGE WHICHCOMPRISES INTRODUCING HOT COKED MATERIAL INTO A DECOMPOSITION ZONE,IMMEDIATELY SPREADING SAID HOT COKED MATERIAL TO FORM A LAYER HAVING ANAVERAGE THICKNESS OF ABOUT ONE TO ABOUT NINE INCHES, SPRAYING ATOMIZEDSULFURIC ACID SLUDGE ONTO SAID LAYER AT THE POINT OF ENTRY OF SAID HOTCOKED MATERIAL INTO SAID DECOMPOSITION ZONE TO COAT SAID HOT COKEDMATERIAL WHILE MAINTAINING A SPRAY CONE PATTERN OF ABOUT 88* TO ABOUT92*, ONE EDGE OF SAID CONE BEING SUBSTANTIALLY PERPENDICULAR TO SAIDLAYER, MAINTAINING THE TEMPERATURE IN SAID DECOMPOSITION ZONESUFFICIENTLY HIGH TO SUBSTANTIALLY COKE THE MAJOR PORTION OF THEHYDROCARBON MATERIAL IN SAID SLUDGE AND OBTAIN GASEOUS DECOMPOSITIONPRODUCTS, REMOVING SAID GASEOUS DECOMPOSITION PRODUCTS FROM SAID GASEOUSDECOMPOSITION ZONE, REMOVING COKED MATERIAL FROM SAID DECOMPOSITION ZONEAND RECYCLING A PORTION OF SAID LATTER COKED MATERIAL TO CONSTITUTE THEHOT COKED MATERIAL COATED WITH THE SULFURIC ACID SLUDGE.